Back in 1958, at the dawn of the space age, physicist James Van Allen discovered that the Earth is ringed by high-energy charged particles. Held in place by the planet’s magnetic field, these bands of radiation were named the inner and outer Van Allen Belts. They’re of particular interest to NASA as they pose a potential danger to spacecraft.

Now a NASA mission also named for Van Allen has found something new about his belts. By looping through them repeatedly, the twin Van Allen Probes discovered a third band of radiation.

But the new structure is no longer. Four weeks after the probes found it, the third ring was wiped out by a strong shock wave emanating from the sun. Still, the unexpected finding shows that the Van Allen Belts are more complex and variable than had been assumed. And that seemingly well-established knowledge about space still may have the capacity to surprise.

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